Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2010
Publication Date: 10/4/2010
Publication URL: http://handle.nal.usda.gov/10113/53699
Citation: Dell, C.J., Meisinger, J.J., Beegle, D.B. 2010. Subsurface application of manure slurries for conservation tillage and pasture soils and their impact on the nitrogen balance. Journal of Environmental Quality. 40(2):352-361. Interpretive Summary: The incorporation of manures into soil with tillage is frequently recommended to reduce losses of nitrogen as ammonia and to provide other benefits, such as reducing odor and phosphorus losses in runoff water. However, incorporation with tillage is not compatible with many soil conservation practices for croplands (such as no-till production) and is not possible with pasture or perennial forage crops. Manure injection technologies allow incorporation with limited disruption of the soil surface or plant cover. This paper reviews the benefits and potential negative consequences of manure injection, with respect to the fate and utilization of manure nitrogen. Numerous publications have shown that the injection of liquid swine and diary manures can reduce nitrogen losses due to ammonia emissions by at least 40%, relative to surface application, and often by 90% or more. However, injection can create anaerobic soil conditions that favor denitrification (microbial conversion of nitrate to nitrous oxide or dinitrogen) leading to greater gaseous losses of nitrogen. The limited number of studies that have measured nitrogen losses from denitrification showed that as much as 50% of the nitrogen that is conserved by reducing ammonia emissions can later be lost as dinitrogen gas (benign) or the potent greenhouse gas nitrous oxide. While the potential for greater nitrous oxide emissions with manure injection has been shown, more extensive research is needed to understand the magnitude of the impact on nitrous oxide emissions. There is also concern that manure injection may also increase nitrate leaching, but research indicates that greater leaching is not likely to be a problem if manure is applied at recommended rates. Plant utilization of nitrogen conserved by reducing ammonia emissions was shown in only a portion of the published studies, indicating that further work is needed to better synchronize manure N availability and crop uptake. Manure injection is expected to lead to a net reduction in nitrogen losses even with increased denitrification. However, further environmental and economic analysis is needed to determine to what extent the potentially greater nitrous oxide emissions offset benefits derived from subsurface manure injection.
Technical Abstract: Manure injection provides for soil incorporation of manures in no-till and perennial forage production. Injection is expected to substantially reduce nitrogen loss due to ammonia volatilization, but a portion of that N conservation may be offset by greater denitrification and leaching losses. This paper reviews our current knowledge of the impacts of subsurface application of cattle and swine slurries on the nitrogen balance and outlines areas where a greater understanding is needed. Numerous publications have shown that liquid manure injection using disk openers, chisels, or tines can be expected to reduce ammonia emissions by at least 40%, relative to broadcast application, and often by 90% or more. However, the limited number of studies that have also measured denitrification losses have shown that increased denitrification with subsurface application can offset as much as half of the N conserved by reducing ammonia emissions. Since the greenhouse gas nitrous oxide is one product of denitrification, increases in its emission require further consideration. Subsurface manure application generally does not appear to increase leaching potential when manure is applied at recommended rates. Plant utilization of conserved N was shown in only a portion of the published studies, indicating that further work is needed to better synchronize manure N availability and crop uptake. At this time in the US, the benefit from reducing losses of N as ammonia are expected to outweigh potential increases in denitrification with subsurface manure application. However, further environmental and economic analysis is needed to determine to what extent the potentially greater nitrous oxide emissions offset benefits derived from subsurface manure injection.